How can I automatically extend edge loop selection?
Since the target edges are all boundaries, there are multiple ways to do this:


AltRMB twice on a boundary extends the selection to all boundary edges.For single boundary loop as shown in the example


Other ways to select boundaries. 


In Vertex Select or Edge Select mode: 3D View menu > Select -> Non Manifold (or press ShiftCtrlAltM).
Or you can first select all elements, then go to 3D View menu > Select > Select Boundary Loop.